When you register to vote in the US you have the opportunity to register a political preference for primary election purposes. Whether or not you are a member of the political party you register a preference for is of no relevance. You are exercising your right, as a member of the American electorate, to participate in the selection of the candidates who contend elections.
This is a right that is denied to members of the British electorate where candidate selection (the real election in most constituencies) is restricted to political insiders. The primary system allows, say, a Republican supporter in a safe Democratic seat to register as a Democrat and to participate in the selection of the Democratic candidate who will inevitably be elected. In this way all electors can try to select a candidate with whom they agree on some issues. If candidates for London mayoral elections really were to be selected by US-style primaries then London politics would become truly interesting.
London W2Reuse content